The Giant Cretaceous Coelacanth (Actinistia, Sarcopterygii) Megalocoelacanthus dobiei Schwimmer, Stewart & Williams, 1994, and Its Bearing on Latimerioidei Interrelationships Hugo Dutel1,2*, John G. Maisey3, David R. Schwimmer4, Philippe Janvier1, Marc Herbin2, Gae¨l Cle´ment3 1 UMR 7207 CNRS-MNHN, Centre de Recherches sur la Pale´obiodiversite´ et les Pale´oenvironnements (CR2P), De´partement Histoire de la Terre, Muse´um national d’Histoire naturelle, Paris, France, 2 UMR 7179 CNRS-MNHN, Me´canismes adaptatifs: des Organismes aux Communaute´s, De´partement E´cologie et Gestion de la Biodiversite´, Muse´um national d’Histoire naturelle, Paris, France, 3 Division of Paleontology, American Museum of Natural History, City of New York, New York, United States of America, 4 Department of Earth and Space Sciences, Columbus State University, Columbus, Georgia, United States of America Abstract We present a redescription of Megalocoelacanthus dobiei, a giant fossil coelacanth from Upper Cretaceous strata of North America. Megalocoelacanthus has been previously described on the basis of composite material that consisted of isolated elements. Consequently, many aspects of its anatomy have remained unknown as well as its phylogenetic relationships with other coelacanths. Previous studies have suggested that Megalocoelacanthus is closer to Latimeria and Macropoma than to Mawsonia. However, this assumption was based only on the overall similarity of few anatomical features, rather than on a phylogenetic character analysis. A new, and outstandingly preserved specimen from the Niobrara Formation in Kansas allows the detailed description of the skull of Megalocoelacanthus and elucidation of its phylogenetic relationships with other coelacanths. Although strongly flattened, the skull and jaws are well preserved and show many derived features that are shared with Latimeriidae such as Latimeria, Macropoma and Libys. Notably, the parietonasal shield is narrow and flanked by very large, continuous vacuities forming the supraorbital sensory line canal. Such an unusual morphology is also known in Libys. Some other features of Megalocoelacanthus, such as its large size and the absence of teeth are shared with the mawsoniid genera Mawsonia and Axelrodichthys. Our cladistic analysis supports the sister-group relationship of Megalocoelacanthus and Libys within Latimeriidae. This topology suggests that toothless, large-sized coelacanths evolved independently in both Latimeriidae and Mawsoniidae during the Mesozoic. Based on previous topologies and on ours, we then review the high-level taxonomy of Latimerioidei and propose new systematic phylogenetic definitions. Citation: Dutel H, Maisey JG, Schwimmer DR, Janvier P, Herbin M, et al. (2012) The Giant Cretaceous Coelacanth (Actinistia, Sarcopterygii) Megalocoelacanthus dobiei Schwimmer, Stewart & Williams, 1994, and Its Bearing on Latimerioidei Interrelationships. PLoS ONE 7(11): e49911. doi:10.1371/journal.pone.0049911 Editor: Daphne Soares, University of Maryland, United States of America Received August 7, 2012; Accepted October 15, 2012; Published November 27, 2012 This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Funding: GC and DS were supported by the American Museum of Natural History (AMNH) Axelrod Fund for his visit in the AMNH fossil fish collection to work on the herein described material. This work was partly supported by the French Agence Nationale de la Recherche under the TERRES Project (ANR-2010-BLAN-607- 03). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: [email protected] Introduction features evolved independently in Mawsonia and Megalocoelacanthus. The authors have suggested that Megalocoelacanthus is closer to Megalocoelacanthus dobiei Schwimmer, Stewart & Williams, 1994 is Macropoma and Latimeria than to Mawsonia. However, their a giant marine coelacanth discovered in 1987 [1] in the Upper assumption was only based on the comparison of meristic data Cretaceous Bluffown Formation, southeastern USA. With an of some anatomical features (table 2 in [1]), but not on a estimated length of 3.5 m, Megalocoelacanthus is among the largest phylogenetic analysis. known coelacanths. Similar dimensions (i.e. more than 2.0 m in Since its discovery, the relationships of Megalocoelacanthus with total length) are reached by the late Jurassic-mid Cretaceous genus other coelacanths have never been investigated. Here we present a Mawsonia from North Africa and South America [2–7], and the description of cranial and postcranial skeleton of Megalocoelacanthus Early Cretaceous genus Axelrodichthys from Brazil [5] also attained based on new and holotype material. A phylogenetic analysis of 39 a large size. Previous phylogenetic analyses [8–14] supported a taxa and 110 characters is performed to clarify the position of sister-group relationship of Mawsonia and Axelrodichthys within Megalocoelacanthus among coelacanths, and its bearings on Meso- Mawsoniidae Schultze, 1993 [15]. This close affinity between zoic coelacanth’s interrelationships are subsequently discussed. toothless, large-sized Mesozoic coelacanths raised the question Implications for the coelacanth taxonomy will also be discussed whether these features could be synapomorphies of a putative and the application of phylogenetic definitions to coelacanth clade or have evolved independently in several lineages. The taxonomy will be proposed based on our novel topology. evolution of large sized, toothless coelacanths has been briefly discussed by Schwimmer et al. [1] who suggested that these PLOS ONE | www.plosone.org 1 November 2012 | Volume 7 | Issue 11 | e49911 The Giant Cretaceous Coelacanth Megalocoelacanthus Materials and Methods ethmosphenoid and otoccipital portions), snout, lower jaws, gular plates, branchial arches, urohyal, hyoid skeleton, and shoulder 1. Geological context girdle. Although most of these isolated remains are strongly Megalocoelacanthus remains are known only from the United flattened laterally, they are outstandingly preserved. Significant States. The holotype CCK 88-2-1 consists of cranial and elements from the holotype specimen CCK 88-2-1 are also branchials elements [1], and was found in the lower part of the included in the description for further comments. Blufftown Formation in eastern Alabama, that is early Campanian in age (Figure 1). Remains of Megalocoelacanthus were also first 3. Nomenclatural Acts reported in five additional regional localities from the southeastern The electronic version of this document does not represent a states of Alabama and Georgia [1], along with a single coronoid published work according to the International Code of Zoological fragment from New Jersey. Subsequently, unpublished specimens Nomenclature (ICZN), and hence the nomenclatural acts have been collected in coeval strata in Mississippi (Schwimmer, contained in the electronic version are not available under that Earl Manning, pers. comm.), and Kansas. All known fossils of Code from the electronic edition. Therefore, a separate edition of Megalocoelacanthus with well-known stratigraphic associations are of this document was produced by a method that assures numerous late Santonian to mid-Campanian age [1], except the New Jersey identical and durable copies, and those copies were simultaneously specimen which is in a late Campanian-early Maastrichtian obtainable (from the publication date noted on the first page of this deposit. However, the latter fossil is a highly ablated principal article) for the purpose of providing a public and permanent coronoid fragment, preserved in a near shore lag deposit, which scientific record, in accordance with Article 8.1 of the Code. The may have been reworked from older material: its age is thus separate print-only edition is available on request from PLoS by uncertain. sending a request to PLoS ONE, Public Library of Science, 1160 Battery Street, Suite 100, San Francisco, CA 94111, USA along 2. Material with a check for $10 (to cover printing and postage) payable to This redescription of Megalocoelacanthus is mainly based on ‘‘Public Library of Science’’. AMNH FF 20267, which was collected in 2007 in the Niobrara In addition, this published work and the nomenclatural acts it Formation, in the Northern Lane County, Kansas (Figure 1). It is contains have been registered in ZooBank, the proposed online early Campanian in age and thus approximately coeval with the registration system for the ICZN. The ZooBank LSIDs (Life holotype CCK 88-2-1. The new specimen consists of skull (both Science Identifiers) can be resolved and the associated information Figure 1. Geological context of Megalocoelacanthus dobiei Schwimmer, Stewart & Williams, 1994. Left, white star indicates the geographic location of the locality of AMNH FF 20267 in the Niobrara chalk of Lane County Kansas, USA (modified from http://www.kgs.ku.edu/ General/Geology/County/klm/lane.html). Right, stratigraphic correlation chart between the principal stratigraphic units from North America (taken from [1]). The Niobrara Formation in Lane County, Kansas, is correlated with the Blufftown, Mooreville, and Eutaw Formations in Alabama and Georgia, where the first